The present invention relates generally to laser imaging assemblies and laser imaging systems incorporating such assemblies. In particular, the present invention relates to a small, low input power, high-resolution direct laser imaging system which utilizes a demagnification optical assembly providing high power density at the media surface and which may be precisely controlled for scanning within an x-y coordinate system.
Laser imaging systems are commonly used to produce photographic or electrophotographic images from digital image data generated by computer-controlled or microprocessor-based scanner systems. The digital image data is a sequence of digital image values representative of the scanned image, Image processing electronics within an image management subsystem processes the image data values to generate a sequence of digital laser drive values (i.e., exposure values), which are input to a laser scanner. The laser scanner is responsive to the digital laser drive values for scanning across the photosensitive film or an electrophotographic drum in a raster pattern exposing the latent image on the film or drum surface. In either of these systems, further development is required to obtain a useful image.
Optical scanning assemblies are used to provide uniform exposure of the image on photosensitive film. The optical scanning assemblies combine a laser system with unique optical configurations (i.e., lenses and mirrors), for uniform exposure of the image onto the film. Such systems combine complex, multi-sided mirrors and lens configurations for directing and magnifying the laser beam as it is scanned across a moving or stationary photosensitive film.
One known laser imaging system includes a polygon mirror scanner. The polygon mirror scanner configuration has a polygon mirror which repetitively exposes successive raster lines or scan lines across a sheet of moving photosensitive film or electrophotographic media. The scan lines extend across the entire sheet. The film can be held stationary, moved at a constant speed, or in stepped increments after each successive scan line. Such scanning systems are rather large and require optical assemblies for focusing, directing, and magnifying the laser beam at the film surface, across the entire surface of the sheet.
For example, known electrophotographic imaging systems require very low laser energy of less than 500 microjoules/cm2. This allows for the use of optical assemblies having magnification factors between 5 and 30 times for magnification of the laser beam. Certain films or media surfaces (e.g., black aluminum suboxides) require significant beam energy (more than 10 millijoules per cm2) for forming an image. In order to provide this much energy in a reasonable time frame, the beam energy density must be at least 50 cm/killowatt2 to form a direct image. In systems with this magnitude of power, light amplification techniques are required (e.g., See U.S. Pat. No. 5,822,345, entitled xe2x80x9cDiode-Pumped Laser System and Methodxe2x80x9d). It is very difficult to achieve significant beam energy at media surfaces for laser imaging systems having high magnification factors, within a compact laser scanner system.
Multimode laser diodes are generally considered not suitable for laser imaging systems incorporating scanner assemblies. Multimode laser diodes have wide orifices or emitters resulting in undesirably large spot sizes. Multiple wavelengths emitted from such diodes have resulted in diffractive errors.
The present invention provides a laser imaging system for direct imaging with high optical power a series of pixels forming an image on a media surface. The laser imaging system includes a laser light source, wherein the laser light source emits a laser beam representative of the image to be scanned on the media surface. An optical path is defined between the laser light source and the media surface. A scanner is provided having a mirrored surface positioned along the optical path. An optical assembly is positioned along the optical path for shaping and focusing the laser beam at the media surface, including an F-Theta lens assembly positioned along the optical path between the scanner and the media surface. The F-Theta lens assembly including a spheric lens, an aspheric lens and a toric lens, providing an increase in optical power density at the media surface.
In another embodiment, the present invention provides an imaging system for direct imaging with high optical power density a series of pixels forming an image on a media surface. The system includes a first imaging module including a collimated laser light source, wherein the laser light source emits a multimode laser beam representative of the image scanned on the media surface. An optical path is defined between the laser light source and the media surface. A scanner is provided having a mirrored surface positioned along the optical path, the scanner being rotatable about an axis of rotation for producing a scan line on the media surface. An optical assembly is positioned along the optical path for shaping and focusing the collimated laser beam at the media surface. The optical assembly includes an F-Theta lens assembly positioned along the optical path between the scanner and the media. The F-Theta lens assembly including a spheric lens, an aspheric lens and a toric lens, providing an increase in power density at the media surface. A first mechanism is provided for translational movement of the first imaging module in a first direction along the axis of rotation of the scanner during operation of the laser imaging system. In one aspect, a feeder mechanism is provided for imparting relative movement between the scanner assembly and the media surface in a direction substantially perpendicular to the rotational axis of the scanner assembly. The feeder mechanism timing is coordinated (i.e., synchronized) with the scanner and translational mechanism.